Drinking cups and handheld containers with leak tight top-covers, combined with drip-less spout and air vent are provided throughout the years in many shapes and forms, in order to prevent spilling of the liquid, contained therein for temporarily storage. The spout and vent are provided with valves that enable fluid to be withdrawn from the container or cup, when someone sucks on the spout. The reduction in fluid content in the container is replaced by air that flows through a second opening in the cover. This air vent holds a valve that opens when the pressure drops below the atmospheric outside pressure, due to the suction action at the spout. As an example; a drip less feeding/training container of this nature has been described by Belanger in U.S. patent description U.S. Pat. No. 5,079,013; U.S. Pat. No. 5,542,670 by Morano; U.S. Pat. No. 5,186,347 by Freeman etc. For all these inventions the application was primarily made for babies and toddlers with the objective of eliminating spillage of the fluid by overturning the cup or container and while drinking during movement. In the above patent descriptions other references are made to other inventors, all with the same or similar goals in mind of eliminating spillage of fluid.
The thus described applications are suitable for non-carbonized fluids and cold drinks only. If carbonized fluids are used, the pressure in the container will built-up thereby pushing the valve open and leakage and spilling is not prevented. The same applies to hot drinking fluids, whereby the air above the fluid is heated and expands, causing the pressure in the container to rise thereby causing the fluid to move out, if not held in the upright position. Spilling could be prevented, however, by using a stronger resilient valve material in the case of Morano U.S. Pat. No. 5,542,670 or a stronger spring in the case of Belanger, U.S. Pat. No. 5,079,013. The draw back, however, is that suction on the spout has to increase appreciably, even beyond human capacity while opening of the valve would become impossible or at least cumbersome.
For beverage cans, as nowadays are commonly available to the consumer with carbonized drinking fluids, adapters are provided that clips onto the top of the can to close off the beverage can after opening and/or make drinking easier than directly from the can. Such features are provide for in the following patent descriptions: U.S. Pat. No. 4,796,774 by Nabinger; U.S. Pat. No. 4,852,776 by Patton; U.S. Pat. No. 4,883,192 by Krugman; U.S. Pat. No. 5,071,042 by Esposito, U.S. Pat. No. 5,947,324 by Palinchak, EP 0870 685 A1 by Igor etc. These applications have the disadvantage that the pressure is immediately released from the can after opening and in the shortest possible time the carbon dioxide is released from the fluid and becomes flat and much less attractive to drink. This means that all previous described applications are not suitable for carbonized beverages or hot drinking fluids. A major improvement to the above problems has been provided in U.S. Pat. No. 6,290,090 of Essebaggers, whereby a valve that closes off the drinking fluid, is opened by a membrane. This membrane enables the valve to be closed by a much stronger spring (or the resilient force of the membrane itself) than in earlier solutions, as the surface area on which the suction pressure operates to open the valve, has been substantially increased. The allowable pressure in the container can be increased appreciably over the previous solutions, before leakage occurs. The magnitude of the allowable pressure in the container, however, has a direct relation with the stiffness of the spring and subsequently the surface area of the membrane. This means that with a certain diameter (surface area) of this membrane there is a limit to the stiffness of the spring that keeps the valve closed and at the same time to enable a human to suck the valve open.
The present invention overcomes the latter problem by inverting the membrane, which now pushes the valve open rather than pulling, thereby combining a number of advantages over prior art solutions. This means that the spring stiffness has no relation with the internal gas pressure of the container and for that matter a very weak spring can be used, just adequate to pull the valve closed. If the gas pressure increases, the valve will be pushed onto its seat by the internal gas pressure instead of being opened as for the earlier solution as described in patent U.S. Pat. No. 6,290,090 of Essebaggers. This means that as long as the internal gas pressure is higher than atmospheric, the valve will be forced closed, while when the internal pressure drops below the atmospheric pressure (by emptying the container), air can enter through the same valve thereby reducing the vacuum and making fluid extraction more easy.